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A Novel Three-Dimensional Model of Basal-like Breast Cancer
Tumor Cell Biology V
Background: Recent studies have identified a new subtype of breast cancer, the basal-like group, which expresses genes characteristic of basal epithelial cells and is associated with poor clinical outcomes. However, the genes responsible for their aggressive behavior are unknown. Identification of these genes could lead to new therapies for basal-like tumors. We have recently demonstrated that the heat shock protein a B-crystallin is expressed in approximately half of basal-like breast carcinomas and independently predicts poor survival. We have also shown that overexpression of a B-crystallin transforms immortalized human mammary epithelial cells (MECs) and induces neoplastic-like changes in mammary acini grown in three-dimensional (3D) basement membrane culture, an in vitro system that more faithfully models human breast tumors in vivo than conventional 2D tissue culture. Moreover, immortalized MECs overexpressing a B-crystallin form mammary carcinomas in nude mice that recapitulate features of basal-like tumors. However, the mechanisms by which a B-crystallin transforms MECs is poorly understood, and it is also unclear whether continued expression of a B-crystallin is required for tumor maintenance and progression. Hypothesis: We hypothesize that a B-crystallin is a key mediator of the aggressive phenotype of basal-like breast tumors and that inhibition of a B-crystallin will suppress the transformed phenotype and growth of these tumors. We will also use our novel 3D model to decipher the oncogenic mechanisms of a B-crystallin. Specific Aims: (1) To determine the dependence of basal-like breast tumors on a B-crystallin expression in 3D culture and in vivo ; (2) To determine the gene expression profile of MECs overexpressing a B-crystallin in 3D culture and in vivo ; and (3) To screen a library for short hairpin (sh) RNAs that suppress the neoplastic phenotype conferred by a B-crystallin in 3D culture. Study Design: These aims will be accomplished by silencing a B-crystallin (RNAi) and examining the effects in 3D and xenograft models (aim 1), by performing cDNA microarray analyses of 3D and xenograft models (aim 2), and by identifying shRNAs that inhibit the oncogenic actions of a B-crystallin in 3D culture (aim 3). Potential Outcomes/Benefits: These studies will provide new insights into the pathogenesis of basal-like breast cancer and may lead to the identification of novel drug targets for these aggressive tumors, which are often refractory to existing therapies.
Recent studies have identified a new type of breast cancer, the so called basal-like tumors, which account for 15% of breast cancer cases and have a poor prognosis. However, the gene(s) responsible for their aggressive behavior are unknown. We have recently demonstrated that a protein called a B-crystallin is commonly expressed in these tumors and predicts poor survival in breast cancer patients. We have also demonstrated that introducing this gene into non-cancerous breast cells transforms them into breast cancer cells, which form breast tumors that resemble human basal-like tumors when injected into mice. In addition, we have used a powerful new technique to grow normal breast cells as three-dimensional (3D) gland-like structures that are similar to those present in the normal breast. However, when we introduce a B-crystallin into non-cancerous breast cells, these cells start growing uncontrollably and form enlarged 3D masses that resemble breast tumors. Importantly, this 3D breast cancer model is much more representative of real breast tumors in patients than conventional cell culture models, making it an ideal system to study molecular mechanisms of breast cancer. Although our results suggest that a B-crystallin plays a role in causing basal-like tumors, we do not how a B-crystallin transforms non-cancerous breast cells into breast cancer cells and whether blocking a B-crystallin will prevent tumor growth. Our hypothesis is that inhibiting a B-crystallin will prevent the growth of basal-like tumors. In aim 1, we will block the expression of a B-crystallin by so called RNA interference and examine the effects on basal-like breast tumors in 3D culture and in mice. In aim 2, we will identify genes that are regulated by a B-crystallin in basal-like breast tumors in 3D culture and in mice by a technique called cDNA microarray analysis. In aim 3, we will block the expression of many different genes by RNA interference and examine the effects on 3D basal-like breast tumors expressing a B-crystallin. This approach will identify genes that are required by a B-crystallin to cause basal-like tumors, and these genes represent possible new drug targets to treat these tumors. These studies, then, will use a novel 3D culture and mouse model of basal-like breast cancer to discover the underlying causes of these tumors. In addition, these experiments may lead to the identification of new drug targets for these aggressive tumors, which often do not respond to current treatments.